Steel frame, damaged rear mech thread - tap or helicoil?

Airmiles
Airmiles Posts: 101
edited July 2007 in Workshop
I've been a gumby, and cross-threaded the rear mech on my commuter. :cry:

My LBS sort-of re-cut the thread & it was OK for a while, but now the rear mech is ~15 deg out of line with the chain.

So - re-cut the thread, fill with weld & re-cut, or helicoil? Frame is Columbus Cyber (old Kona hardtail)

Doesn't a helicoil rely on the (damaged ) original thread still being straight?

I believe Argos could sort this, but they're in Bristol & I'm in S London. Roberts maybe? But they don't mention repairs on their site...

Thanks

Miles
I'm not saying pedestrians in Hackney are stupid.. but a fixed bayonet would be more use than a fixed gear...

Comments

  • MarvintheAndroid
    MarvintheAndroid Posts: 409
    The old thread wouldn't matter if you fit a helicoil, as you would need to drill out and tap a larger diameter to fit the insert. However (being no expert) I suspect that welding may turn out to be the best option - even though it would of course damage the paint finish.

    Try here http://www.portobellovillage.com/bicycle/default.asp

    Marv
    What tree ? ...........

    Trek 8000 ZR XC hardtail.
  • Monty Dog
    Monty Dog Posts: 20,614
    Many motorbike or engine repair places may offer Helicoil repairs - it's quite common with aluminium crankcases and blocks. Drill the hole out to the required size, use the right size tap to cut a new thread before fitting a Helicoil insert.
    Make mine an Italian, with Campagnolo on the side..
  • John.T
    John.T Posts: 3,698
    Helicoil. Welding will affect the structure of the steel and could well weaken it. Make sure the hole is tapped straight or the mech will not hang right. I would not use the bike much until it is repaired as the mech may drop off.
    My Fleet.
  • nick hanson
    nick hanson Posts: 1,655
    Stating the obvious here,but do make sure you can get the correct size helicoil,before drilling out,as a lot of bike thread sizes are none standard
    so many cols,so little time!
  • nicklouse
    nicklouse Posts: 50,673
    welding would be a bad idea. ever tried drilling a weld?

    you dont want to.

    helicoil. thread sert to name two.

    but most LBS's will have a thread saver of some sort.

    here is something for a badly damaged drop out.


    http://www.ison-distribution.com/ison/e ... rt=2IDGHS3

    2idghs-d-out-insert.jpg
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • bike_the_planet
    bike_the_planet Posts: 260
    So - re-cut the thread, fill with weld & re-cut, or helicoil? Frame is Columbus Cyber

    Best to tap out and helicoil.

    Some steel frame alloys are very particular about weld temperature. Some, such as Reynolds 531, cannot even be welded - they must be brazed.

    If you're still considering the weld option, then take it to a good framebuilder/repairer such as Roberts in South Croydon. They will know how to handle the job.

    Cheers
    BTP,

    Perth, WA

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